The present invention relates generally to a voice override and amplitude control circuit for an audio entertainment system, and more particularly to a voice override and amplitude control circuit which gradually suppresses a normal music signal to allow the normal music signal to be overridden by a voice signal and which gradually returns the music signal to its full strength at the conclusion of the voice signal.
In the offices of doctors and dentists and the like, it is common practice to provide music for the enjoyment of the patients awaiting their appointments and others in the waiting rooms and for the relaxation of patients while undergoing treatment as in a dentist chair, for example. It is further common practice to provide a public address system for calling patients or making other announcements to those in the waiting rooms or for providing instructions or the like to patients undergoing treatment. The communication system utilized may be either two separate systems, one for the music and one to serve as the public address system or a single system may be used for both the music and voice communications. One or more speakers are utilized in larger, more public areas, such as a doctor's waiting room, while individual systems such as headphones and the like are provided for patients undergoing treatment.
Typically, such a system is set up to provide music for the majority of the time while allowing the music to be suppressed when it is desired transmit a voice signal to effect communication with a patient or others. It is known in the prior art to provide means, such as manual switches or automatic muting circuitry, to allow the music signal to be overridden by a voice signal. However the transition from music to voice, and back again, is abrupt. Further, most systems suppress the music completely when transmitting a voice signal. Under certain conditions, it is highly desireable that a patient not make sudden movements while undergoing treatment, such as a patient in a dentist chair. When a dentist interrupts the music to provide instructions or speak to a patient under treatment, the abrupt transition from music to voice may startle a relaxed patient thereby causing the patient to move suddenly and disrupt the treatment or even cause injury to the patient.
U.S. Pat. No. 3,518,375 entitled "Voice Override Circuit" issued on June 30, 1970 to William R. Hawkins discloses an audio system in which a voice signal from a microphone automatically suppresses the normal signal which resumes after the voice signal terminates. The normal music signal is applied across a voltage divider circuit that comprises a first resistor, the collector and emitter of a transistor and an emitter load resistor. When the transistor is off, i.e., non-conductive, its impedance is very high compared to the first resistor and substantially the full signal strength of the music signal is applied to an audio amplifier and speaker system. When a microphone signal of sufficient strength is present, the transistor switches on and the music signal input to the amplifier is reduced by an amount dependent upon the ratio of the values of the first resistor and the emitter load resistor. At the same time, a capacitor is quickly charged and maintains the transistor in a conductive state. When the microphone signal terminates, the capacitor discharges and the transistor switches off when the capacitor potential drops below the required transistor base bias voltage and the full, normal music signal is again applied to the amplifier. The transistor acts as a switch, abruptly suppressing the normal music signal and transmitting the full strength voice signal to the speaker system. Similarly, when the voice signal terminates, after a short delay, the music signal is abruptly returned to its full strength.
Primarily, it is an object of the present invention to provide an audio system providing a normal music signal which may be gradually overridden by a voice signal, the music signal being gradually attenuated a predetermined amount and the voice signal strength gradually increased to a level determined by a volume setting and the music signal gradually returning to its normal level upon termination of the voice signal.